1. Field of the Invention
The present invention relates to a structure of a magnetic head slider and a method for producing such magnetic head slider, and more particularly to improvements in a negative-pressure type magnetic head slider suitable for a magnetic disk drive capable of high-density recording, and improvements in the method of production of such negative-pressure type magnetic head slider.
2. Discussion of the Prior Art
In a rigid magnetic disk drive (RDD), a magnetic head is formed integrally with a slider which is adapted to be held apart from a rotating magnetic disk, by a suitable small distance, so that the magnetic head is operable to record and reproduce (write and read) information on and from the magnetic disk while the magnetic head maintains a suitable flying height or air bearing clearance or gap of about 0.2-0.3 .mu.m with respect to the disk surface. The rigid magnetic disk drive is widely used as an external storage device for a computer, owing to relatively high density of recording per unit area of the magnetic disk, comparatively short access time, and considerably high rate of transfer of information. To further improve the recording density of a magnetic disk used in the rigid magnetic disk drive, there are growing requirements for reducing a flying height between the head slider and the magnetic disk surface, and increasing the stability of maintaining the clearance at a constant value. In an attempt to satisfy these requirements, extensive studies and research have been made to provide a negative-pressure type magnetic head slider which has a high degree of air-bearing stability, i.e., constant amount of flying height between the head slider and the magnetic disk surface.
An example of such negative-pressure type magnetic head slider is indicated generally at 7 in FIGS. 1 and 2. The magnetic head slider 7 has a configuration as shown in FIG. 1, and is operated in a posture as indicated in FIG. 2 with respect to a magnetic recording medium in the form of a magnetic disk 8, on and from which information is written or read by the magnetic head. Namely, the information writing and reading operations are effected while an air stream exists between the surface of the magnetic disk 8 and the operating surface of the head slider which faces the disk 8.
Described more specifically, the operating surface of the magnetic head slider 7 which faces the magnetic disk 8 has a pair of parallel spaced-apart air-bearing portions 1, 1, a cross rail 2, a pressure-reducing or sucking portion 3, and an inclined portion 4 (which may be replaced by a stepped portion 4). The inclined portion 4 is provided at one end of the head slider 7, for positively or effectively introducing an air stream caused by the rotation of the magnetic disk 8, into the space between the disk 8 and the operating surface of the slider 7. The inclined portion 4 terminates in the cross rail 2 in the direction of flow of the air stream, and the cross rail 2 connects the spaced-apart air-bearing portions 1, 1 at the ends on the side of the inclined portion 4. The air-bearing portions 1, 1 have a generally rectangular shape and function to maintain the head slider 7 in the floating posture by the air stream flowing between the air-bearing surfaces 1, 1 and the surface of the disk 8. The cross rail 2 functions to reduce the amount of flow of the air downstream. The sucking portion 3 is defined by the cross rail 2 and the air-bearing portions 1, 1, such that the portion 3 is formed between the two air-bearing portions 1 and the upstream end of the portion 3 is defined by the cross rail 2. The sucking portion 3 functions to produce an air suction of the head slider 7 toward the magnetic disk 8. Thus, the air-bearing portions 1, 1 and the sucking portion 3 cooperate to maintain the flying height through which the air flows during rotation of the magnetic disk 8.
The sucking portion 3 is defined by a rectangular groove having a depth of about 2-10 .mu.m as measured from the air-bearing surfaces 1, 1. The material and structural requirements of the magnetic head slider 7 do not permit this groove 3 to be formed by a machining operation. Usually, the groove is formed in an ion etching process, as disclosed in laid-open Publication Nos. 62-14386 and 62-40604 of Japanese Patent Applications.
However, the ion etching process suffers from some drawbacks when the magnetic head slider 7 is formed of a ferrite polycrystal. That is, the etching speed is as low as 0.02-0.03 .mu.m/min, taking about one hour or more to form the groove 3, where the argon ion etching is employed, for example. Further, the ion etching process requires a mask for covering the air-bearing portions 1 and the cross rail 2. The mask should be formed of a material which is etched at a lower rate than the ferrite used for the head slider. Alternatively, the mask should have a considerably large thickness.
A known method of producing a negative-pressure type magnetic head slider is illustrated in FIGS. 3(a) through 3(g). Initially, a ferrite block is mirror-polished as indicated in FIG. 3(a). One of opposite major surfaces of the ferrite block is covered by a sputtered metallic masking material such as Cr and Ti, whose etching speed is about one-fourth of that of the ferrite material, as indicated in FIG. 3(b). The metallic masking material is patterned into an etching mask, by photolithography as indicated in FIG. 3(c) and by etching as indicated in FIG. 3(d). Thus, the process to form the etching mask is rather complicated. Where a ferrite polycrystal is used for the magnetic head slider, an ion etching process is used for forming the pressure-reducing portion, as indicated in FIG. 3(e). In this case, the surface roughness of the formed pressure-reducing portion amounts to as high an Rmax as 0.6 .mu.m. If the depth of the groove for the pressure-reducing portion is small, the roughness of the pressure-reducing surface adversely affects the stability in maintaining a desired amount of flying height between the head slider and the magnetic disk surface.
After the pressure-reducing portion is formed by etching through the metallic mask, the mask is removed as indicated in FIG. 3(f). Finally, the inclined (or stepped) portion is formed adjacent to the cross rail at one end of the pressure-reducing portion.
Another problem is encountered in the process of FIGS. 3, when the metallic mask is formed by photolithography and etching as indicated in FIGS. 3(c) and 3(d). Namely, the dimensions of the metallic mask cannot be accurately controlled. In particular, the width accuracy of each air-bearing portion or surface 1 which influences the amount of flying height of the head slider must be held to within a range of .+-.10 .mu.m.
An alternative method of producing the negative-pressure type magnetic head slider is disclosed in laid-open Publication Nos. 60-229283 and 61-76689 of Japanese Patent Applications. This method includes a step of irradiating a ferrite block with a laser radiation, while the ferrite block is submerged in an etching liquid. Although this step is simpler than the ion etching step, the method in question suffers from a considerably low production efficiency and cannot be practiced on an industrially justifiable basis.